Development of an indirect ELISA based on the recombinant Spm2 protein for detection of tropical theileriosis

Evaluation of sporozoite and macroschizont antigen (Spm2) of Theileria annulata for its diagnostic potential

Theileria are tick-borne apicomplexan parasites, which mainly infect ruminants in tropical and subtropical regions of the world. The present study was directed to investigate the serological methods for the diagnosis of theileriosis in crossbred cattle. Blood samples (n = 176) were collected from the regional cattle populations of Bihar state situated at the Gangetic plains of India. Microscopic examination of blood smears from the cattle revealed the presence of tick-borne infectious organisms (Theileria and Anaplasma) in the region. PCR-based detection of Tams1 (Theileria annulata merozoite surface antigen) gene and the sequencing of 18S rRNA amplicon from the blood samples confirmed T. annulata as the primary causative agent of theileriosis in cattle of the Bihar region. Similarly, the amplification of the msp5 gene confirmed Anaplasma marginale infection. For the large-scale epidemiological investigation, sporozoite and macroschizont (spm2) partial gene from T. annulata was cloned in pET-28a (+) vector and overexpressed in E. coli BL21 cells. Overexpressed recombinant-Spm2 (43 kDa) was purified by Ni-NTA affinity chromatography and was used for immunodetection of theileriosis in cattle serum samples. Sequence analysis of the cloned partial spm2 gene in this study showed multiple SNPs (single nucleotide polymorphisms) in T. annulata. Recombinant-Spm2 antigen was explicitly recognised by the immunoglobulins (IgG) of the cattle naturally infected with Theileria. Further, an indirect enzyme-linked immunosorbent assay (ELISA) was developed using partial r-Spm2 antigen that exhibited high sensitivity (100 %) and specificity (90.9 %). Thus, this study suggests that partial r-Spm2 can be used as a diagnostic antigen for seroepidemiological studies of T. annulata infection in crossbred cattle.

Development and evaluation of a chemiluminescence immunoassay for detecting tropical theileriosis

Tropical theileriosis is a tick-borne lymphoproliferative disease of cattle caused by the apicomplexan parasite Theileria annulata, and leads to substantial economic losses to the livestock industry worldwide. Although various enzyme-linked immunosorbent assays (ELISAs) have been established to detect antibodies against T. annulata infection, a specific, rapid and reliable diagnostic assay is urgently needed for prevention and control of the disease. In the present study, a chemiluminescence immunoassay (CLIA) was developed based on the subtelomeric variable secreted protein (SVSP) of T. annulata as a sero-diagnostic antigen. Following optimization of the CLIA working parameters, the working time of the method was less than 4.5 h. The sensitivity and specificity of the established CLIA was 98.8% and 97.5%, respectively, when the cut-off value of the percent positive (PP) was 26.1% for detecting serum samples (n = 242 T. annulata positive sera, n = 158 T. annulata negative sera). After comparing 180 serum samples from Gansu province, China, the concordance rate between the CLIA and a published rSpm2 ELISA method was 72.8%. In addition, 565 serum samples of cattle collected between 2017 and 2018 from four provinces in China were detected by the CLIA, and the seroprevalence for T. annulata ranged from 53.3% to 67.3% in these regions. Our findings demonstrated that the CLIA has high specificity, sensitivity and reliability, and could be used as a rapid detection assay for epidemiological investigations of T. annulata infection.

Molecular survey of piroplasm species from selected areas of China and Pakistan

Background

Piroplasmosis is an important animal disease that is a major constraint to the development of the livestock industry, often resulting in significant economic losses. Therefore, there is an urgent need to further understand the etiology of this and other tick-borne infections.

Methods

Blood samples were collected from tick-infested animals from the Chakwal, Jhang, and Faisalabad districts of Punjab, Pakistan and from peri-urban areas around Hohhot, Inner Mongolia, China to investigate the presence of Babesia and Theileria species. In total, 450 blood samples were collected with FTA cards from cattle of the study areas of Pakistan; the genomic (g)DNA of one hundred and twenty samples from cattle in Inner Mongolia were provided by the Lanzhou Veterinary Research Institute, China. Following the extraction of gDNA, the 18S rRNA gene (V4 hypervariable region) of piroplasms was amplified in all samples using semi-nested PCR. Positively identified samples were sequenced for the identification of Theileria and Babesia species. The partial full-length sequence of 18S rDNA was amplified for species confirmation of Theileria-positive samples, whereas the RAP-1c gene was amplified for Babesia bigemina-positive samples.

Results

Semi-nested PCR results revealed that 144 (25.26%) samples were positive for piroplasms. Theileria annulata was the most prevalent species (115/144; 20.17%), followed by Theileria orientalis (16/144; 2.80%). Among Babesia, the only species recorded was Babesia bigemina (13/144; 2.28%).

Conclusion

The present study reveals new data on the prevalence of piroplasm species in bovine populations of selected areas of China and Pakistan and their phylogenetic relationships. It is also the first detailed report of T. orientalis from native animals in Pakistan.